The present invention relates to an image processing apparatus and method.
Creating three-dimensional computer models of a real-life object has traditionally been time consuming and expensive, requiring skilled personnel and/or expensive equipment. One reason for this is that it is necessary to determine the relative xe2x80x9cdepthxe2x80x9d of points on the object as well as the relative positions of the points in two dimensions.
Known techniques for creating three-dimensional computer models from real objects fall into one of two categories, namely active techniques in which depth information is obtained by actively sensing the surface of the object, and passive techniques in which depth information is obtained from images of the object.
Examples of active techniques include scanning the object with a pulsed laser beam and measuring the detection time of pulses relative to their transmission time to determine depth information (as in a laser xe2x80x9crangefinderxe2x80x9d), and touching the object at A number of points on its surface with a position-sensitive probe.
In conventional passive techniques, at least two images of the object taken from different camera positions are needed. To construct a three-dimensional computer model from the images, it is necessary to know firstly the location in each image of points which represent the same actual point on the object, and secondly the relative positions from which the images were taken. These are particularly onerous requirements. As a result, in known passive systems, distinguishing marks/calibrations are added to the object or its surroundings to enable matching points to be easily identified in the images, and/or the images are taken from known camera positions.
For example, WO-A-90/10194 discloses a system for measuring strain distribution in an object using the three-dimensional coordinates of points on the object surface calculated from two images of the object. To facilitate the matching of points in the images, a uniform square grid pattern is applied to the object before the images are taken, by electrochemical etching or silk screening. Corresponding points of intersection of the grid lines can then be easily identified in the images. Further, the object is placed on a rotary table which is rotated by a known angle between images, thereby defining the relative camera positions.
U.S. Pat. No. 4,803,645 discloses a system for determining three-dimensional coordinates of points on an object in which a grid or similar periodic pattern is projected onto the object using a light projector, and images of the object are taken using three imaging systems at fixed, pre-defined positions.
WO-A-88/02518 discloses a system for producing a depth map of an object from a plurality of images taken from imaging devices set in a predefined, known configuration. Similarly, U.S. Pat. No. 5,307,136 discloses an automobile distance detection system which determines the range of an automobile using images taken from a plurality of cameras mounted in a predefined, known configuration in the user""s automobile.
GB-A-2244621, WO-A-92/06444 and U.S. Pat. No. 4,695,156 all disclose systems for determining three-dimensional coordinates of points on an object surface from stereo images of the object taken at known camera positions.
In many cases, however, it is inconvenient, expensive, and/or infeasible to provide a reference grid or markings/calibrations on the object or its surroundings, or to take images from known relative positions. Reliable and accurate techniques are then required to match points in the images and/or to calculate the relative camera positions.
Even if reference markings are used, it would be desirable to identify other matching points in the images to give more points with which to calculate the camera positions. This would enable the camera positions to be calculated more accurately and/or would allow fewer reference markings to be used on the object or its surroundings.
Further, even if matching points are identified using reference features, an accurate and reliable technique for determining the positions at which the images were taken is necessary if the images were not taken from known relative positions.
The present invention aims to address one or more of the above problems, and aims to provide an image processing apparatus and method for determining matching features in images of an object and/or an apparatus and method for calculating the positions at which the images were taken.
The present invention provides an image processing apparatus or method in which image data for a plurality of images of an object is processed without using prior information on the relationship between the positions from which the images were taken to identify corresponding object features in the images. Matching features are identified using a first technique, the relationship between the images is determined and its accuracy tested, and, if the accuracy is not sufficient, user-identified features are used to identify matches with a second technique.
The present invention provides an image processing apparatus or method in which image data for a plurality of images of an object is processed without using prior information on the relationship between the positions from which the images were taken to identify corresponding object features in the images. The following steps are iteratively performed until a desired accuracy is achieved: (i) user-identified features are used to identify further matching features and (ii) the accuracy of the further identified features is determined.
Preferably, the accuracy of the matches is determined by calculating the relationship between the imaging positions. Signals defining this relationship are then also produced.
According to the present invention, there is provided an image processing apparatus or method in which image data for a plurality of images of an object is processed without using prior information on the relationship between the positions from which the images were taken to identify corresponding object features in the images. Matching features are identified using a first technique, the relationship between the images is determined, and further matches are identified using a second technique together with the determined relationship.
Preferably, the first technique includes a user identifying features, and the second technique includes the image processing apparatus identifying features.
The present invention provides an image processing apparatus or method in which image data for at least three images of an object is processed without using prior information on the relationship between the positions from which the images were recorded, to determine the relationship. Matching features in first and second images are identified and used to determine the positional relationship between these images. The positional relationship is used to identify at least one additional match in the first and second images, at least one of the additional matches is then matched in a third image and the positional relationship of the third image is determined.
The present invention also provides an image processing apparatus or method in which this process is adapted if corresponding object features in a pair of images are already known, or if the positional relationship between a pair of images is already known.
The present invention provides an image processing apparatus or method in which image data for a plurality of images of an object is processed without using prior information on the relationship between the positions from which the images were taken to identify corresponding object features in the images. Each image is notionally split into regions on the basis of matches defined in input signals, and the mapping of regions between images is determined and used to identify further matches.